Revamp ring explosion on charging them: a ring enchanted to a positive value has a enchantment in 7 chance of “vibrating unexpectedly” or something similar. This is a warning and, like weapon vibration, does not hurt the ring. If you get this message, the ring’s otrapped flag is set. Charging a ring with otrapped set always explodes it.

There is no other way to ascertain the otrapped value of a ring, other than getting this message. A ring that generates at +4 or above has an enchantment in 10 chance of already having otrapped set. Discharging the ring via cursed charging or drain life has a 50% chance of removing the otrapped flag per point lost.